One of the major hazards following a significant earthquake is the danger of explosion and fire as a result of gas escaping from broken pipes. Many safety devices have been proposed to automatically shut off gas flow upon occurrence of an earthquake. Typical examples of such proposals are U.S. Pat. No. 3,890,993 to MacNeilage, U.S. Pat. No. 2,158,753 to Hansen, and U.S. Pat. No. 4,353,383 to Kiesel. All of these prior art devices, however, are commercially impractical because they require a specially constructed gas valve which would have to be installed in the gas line by a skilled plumber. Consequently, relatively few home owners use this type of safety device.